With over 40 medical devices being cleared or approved by the FDA in 2018, it’s clear that medical technology mirrors the behavior of technology in general - it’s evolving rapidly. The FDA approvals for this year encompass a wide range, including stents, sutures, implantable lenses, glucose monitoring systems and artificial heart valves.
These devices vary in purpose, but they all have one thing in common: they face unique thermal challenges. Medical devices - whether for implant, temporary placement in the body, or assisting in the operating room - must all withstand thermal loads. What does this mean for engineers and designers? Here are a few ways they’re making sure that the latest medical developments can take the heat.
Smaller Sizes Bring Concentrated Heat
Laptops and cell phones aren’t the only devices where innovation means shrinking in size. Medical instruments have followed suit and still pack a lot of power. While instruments that are smaller and stronger have clear benefits, like being non-invasive and accurate, they must also be designed to operate in the appropriate temperature ranges.
One of the solutions available is two phase cooling. While there are a few different methods, the goal is to use vapor to transfer heat quickly and efficiently so that it can be more easily dissipated. Heat pipes and vapor chambers both accomplish this goal with great efficiency and higher conductivity than single phase cooling or heat sinks.
Another option developed uses graphite, which has high natural electrical and thermal conductivity. Graphite can be used as a heat spreader, lowering the temperature of hot components and protecting sensitive parts from hot spots. Its ability to evenly distribute temperature quickly helps it act as a space-efficient shield, prolonging the life of sensitive instruments.
Keeping Thermal Noise from Ruining the Picture
Imaging equipment such as magnetic resonance imaging (MRI), computerized tomography (CAT scan), ultrasound, and radiography (X-ray) - are depended upon for speed and accuracy. These scans are in high demand, requiring high uptime and the ability to withstand frequent use. These large and complex machines also bring the challenge of multiple heat sources, such as the power source combined with electronic components. Finally, noise and debris must be controlled, which often rules out use of cooling options such as fans.
Noise in medical imaging, including that caused by thermal influences or cooling mechanisms, can cause images to be difficult to read and even lead to a misdiagnosis. Larger machines require considerable thermodynamic management, which leads to heat pipes being partnered with larger heat sinks. Rack-mounted heat pipe assemblies can also be used to cool smaller, portable medical equipment. The cooling is performed without moving parts, making the equipment both quiet and less prone to failure.
Protecting Precision in Surgical Applications
Neurosurgery is a prime example of a time when accuracy really counts. Precision is gained by using tools like bipolar forceps, which use electricity to cauterize or ablate tissue. But electricity brings heat, and too much heat can cause tissue to stick to the forceps. In surgical applications thermal management must be fast and consistent to prevent fatal errors.
One of the solutions to this problem came from a NASA technology “spinoff” of miniaturized heat pipes. NASA’s original interest in heat pipes was due to the vast differences in temperature in space, particularly when moving from sun to shadow. Heat pipes developed with NASA funding became used in x-rays and, eventually, the bipolar forceps used in brain surgery today.
Whether it’s brain surgery or rocket science, engineers should take several factors into account during the design processes for thermal management in medical equipment. By considering patient contact, usage frequency, operational environment and reliability, designers can select the right thermal management solutions to keep equipment running smoothly and on demand.